This invention relates generally to the field of oil deflector seals for rotating shafts, and in particular to an air-sealed oil deflector that generates and maintains a uniformly distributed seal of filtered air around a rotating shaft to prevent ingestion and build-up of dirt in the oil deflector teeth.
A continual problem in operating large steam turbines has been that of dirt contamination of the bearing lubricating oil system. This contamination, if unchecked, is known to produce highly detrimental effects on bearing performance. Fossil fueled steam turbines are particularly subject to the problem since they frequently operate in an environment contaminated with coal dust and fly ash.
It has been found that contaminants enter the lubricating oil system primarily by being drawn in through the bearing oil seals along with the atmospheric air that is necessary for ventilation of the system oil tank and for oil seal cooling. The bearing oil seals, commonly referred to as oil deflectors, are labyrinth seal arrangements which prevent leakage of lubricating oil from the associated bearing. Contaminated air is drawn in through the seal by the lubricating oil system vacuum, entering through the clearances formed by the oil deflector rings (teeth) and the shaft. In a number of situations, contaminant ingestion has completely clogged the deflector teeth with the result that, in some severe instances, the dirt build-up has been carbonized by high temperatures to the point that shaft damage has occurred.
In the past, some effort has been made by workers in this particular field to seal labyrinth seals with a gaseous fluid under pressure. For example, steam seal systems, compressors, and other rotating equipment have been fitted with seals adapted to receive (and sometimes extract) a pressurized gas. These devices usually contain multiple cavities located along the shaft and use relatively small passages provided in the seal housing, or cavities, to inject the fluid into the tooth area. Because of the high air injection velocities required by these configurations, high pressure and correspondingly high flow horsepower are essential to effect a circumferential seal around the shaft. In some instances, there is some doubt as to whether or not a complete circumferential seal is established around the shaft.
It is, therefore, a principal object of the present invention to provide an air-sealed oil deflector which is capable of preventing ingestion and build-up of contaminants in the oil deflector teeth while allowing the deflector to maintain a high level of oil collecting and sealing performance.
It is a further object of the invention to provide an air-sealed oil deflector which is effective in forming a uniform circumferential seal around a rotating shaft without requiring excessive air pressure and flow, i.e., an air-sealed oil deflector operable without unduly high power consumption.
Still further objects and advantages of the invention will be apparent from the ensuing description.